Starting and unloading device for compressors



B. S. AIKMAN.

STARTING AND UNLOADING DEVICE FOR COMPHESSORS.

APPLICATiON FILED AUG131|1920.

Patented Apr. 18

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iNvENToR BURTON Smm/AN BY;

ATTORNEY NETE@ STATES Parana clasica.

BURTON' S. AIKMAN, 0F MILWAUKEE, WISCONSN, ASSIGNOR T0 NATONAL BRAKE &

ELECTRIC COMPANY, OF MILWAUKEE, WISCONSIN, A CORPORATON OIF WES- GONSIN.

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STARTENG AND UNLOADING DEVICE FOR COMPRESSOR/S.

Specification of Letters Patent. Patented Apu". 118, 1922.

Application led August 31, 1920. Serial No. 407,155.

To all whom it may concern:

Be it known that BURTON S. AIKMAN, a citizen of the United States, residing at Milwaukee, in the county of Milwaukee and State of Wisconsin, have invented new and useful lmprovements in Starting and Unloading Devices for Compressors, of which the following is a specification.

rThis invention relates to apparatus for compressing fluid and more particularly to means for controlling a compressor unloading device for an equipment in which the fluid compressor y is driven by an electric motor continually in driving connection with the compressor.

My invention is particularly adapted for use with single phase commutator motors in which at starting, when the current value is high, brushes are employed so as to operatethe motor as a repulsion motor and when the normal running speed of the motor is reached, the connections are changed, so that the motor thereafter runs as an induction motor. j

The principal object of my invention 1s. to provide means for controlling the unloading of the compressor at starting and'when the current 'low to the motor is excessive.

In the accompanying drawing, Fig. 1 is a sectional viewof a compressor unloading device embodying my invention; and Fig. 2 a diagrammatic view of a fluid compressing equipment with the improved unloading device applied thereto.

As shown in Fig. 2 of the drawing, the apparatus may comprise a fluid compressor 1, in continual driving connection 'with an' electric motor 2, and adapted to compress fluid under pressure into a storage reservoir 3.

i Associated with thel compressor 1, is an unloading device comprising a cylinder 4, containing a piston 5 having a stem 6 for operating the suction or inlet valve -7 of the compressor.

F or operating the unloading device, an electrically controlled mechanism 8vis provided, comprising a magnet coil 9 connected in series with the windings of the compressor motor 2 'and having an armature 10.

In alinement with the armature 10 is avalve 11 carried by a loosely fitted piston 12 subject to the pressure of a spring 17 and having a stem 13 which is adapted to be engaged by the armature 10. The valve 11 controls communication from a pipe 14, leading to the storage reservoir 3, to a passage and pipe 15, leading to the piston chamber 16 of the unloading device.

A volume chamber 18 is 4connected by passage 19 to passage 15, the passage 19 being provided with a restricted exhaust port 20.

The armature 10 is provided with means for adjusting the air gap between the stem 13 and the top of the armature, such as a screw 21, having its head adapted to engage the under side of the armature and having screw-threaded engagement in the cap 22.

In operation, the ail' gap between the armature and the valve stem 13 is adjusted so as to require a current fiow in the coil 9 of a certain desired amount in excess of the full speed current flow of the motor in order to operate the armature, for example, a current value of one and one-half times full load current.

When the motor circuit is closed, the starting current will be high and suilicient to cause the armature 10 to be moved toits full upward position. actuated by the armature to open the valve 1l, so that fluid under pressure from the reservoir 3 is supplied from pipe 14, past the valve 11 and around the loose fitting piston 12 to passage 15 and the piston vchamber 16 of the unloading device. The piston 5 is then operated by fluid under pressure to open the suction valve 7 of the compressor, so that the compressor will run without load.

In its upper position, the piston 12 seats, so as to cut off communication from passage 15 to the exhaust port 20 and the chamber 18, so that only the small volume of the piston chamber 16 has to be supplied with fluid from the reservoir 3 and consequently the piston 5 will be actuated. also simultaneously with the opening of the valve 11, thus causing the prompt unloading of the compressor.

Ji/'hen the pressure in the reservoir 3 has substantially equalized into the piston chamber 16,the piston 12 will be moved slightly The stem 13 is thus from its. upper seat'by the action of spring 17, so that the pressure in piston chamber 16 and above piston 12 tendsto reduce by flow of fluid through the port 20 and into the chamber 18. This reduction in fluid pressure above the IVpiston 12 prevents the piston and the valve 11 vfrom moving to closed position, even though the armature 10 may have dropped by this time.

The valve 11 will now remainopen until lthe chamber 18l has beencharged with fluid close.

VSince it requires less current in the coil 9 to hold the armature 10 in its upper position than 1s required to move same to that position, the armature will not drop until4 the current value has been reduced to a considerable extent, for example, if it requires a` current value of one and one-half times the full load current to move .the armature 'from its vlower position, the armature may be held in its upper position until the current value falls to about three-quarters of the full load current andl until this lower current value is reached, the pneumatic timing feature will not of course come into action. i

Since the pneumatic timing action takes place after the armature 10 has dropped, the

compressor remains unloaded for a time which fully ensures that the brushes of the motor will be shiftedfor running the motor as an induction mo'tor before the compressor is loaded.

If, during the running of thecompressor, the current value should rise above a predetermined point, due to the slowin down of the motor on account of line orotlier-conditions, the compressor will be. automatically relieved of its load by the operation of the armature 1() as previously described in connection with starting, thus permitting the motor to speed up and preventing the shifting of the brushes so that vthe motor will continue lto operate as an induction motor.

Under the above abnormal conditions, the coinpressor will ybe alternately loaded and unloaded, but will operate most of the time in the unloaded State, by reason of the delay introduced by the laggmg action of the armature 10 and the pneumatic delay caused I -by the chamber 18 and the' restricted port 20.

' The valve 1 1 and piston 12 also act as a safety valve, -s1nce upon lanincrease in pressure in the reservoir abovea predetermined I degree, the valve 11 will be lifted against the pressure of spring 17, exposing the full area ofthe piston 1 2 to pressure in the reservoir, so that the plston 12 and valve 11 are quickly shifted to their open position, in which fluid under pressure is supplied to the piston cylinder 16 to effect the unloading of the compressor.

p It will now'jbe seen that the above described apparatus functions to cause the compressor to operatein an unloaded state until the full running speed -is attained, to cause the unloading of the compressor whenever the current value rises to a predetermined degree higher than normal, and to ensure the prompt shifting of the motor brush rigging in changing over from a repulsion to,

an induction motor, while the compressor is running unloaded.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is

1. The combination with a Huid compressor, an electric motor for driving said compressor, and a compressor unlo-ading device, of electrically controlled means for controlling the `operation of said unloading device and responsive to a predetermined rise in current supplied to the motor for effecting the operat1on of said device to unload the compressor.

2. rl`he combination with a fluid compressor and an electric motor for driving said compressor, of a compressor unloading device, means operated upon a predetermined rise in current to the motor for effecting the operation of said device to unload the compressor, and fluid pressure means for delaying the operation of said device vto load the compressor when the current to ,the motor becomes reduced.

3. rlhe combination with a fluid compressor and an electric motor for driving said compressor, of a compressor unloading device including a piston operated bv fluid under pressure, a chamber having a restricted exhaust port, valve means for controllingV communication from said piston to said chamber and from a source of fluid pressure to said piston, and means controlled by an abnormal quantity of current to the motor for operating said valve means.

4. The combination with a'fluid compressor and an Aelectric Lmotor for driving said compressor, of a compressor unloading device including a piston operated by fluid under pressure, a chamber having a restricted exhaust port, asource of fluid under pressure, valve means having a position for connecting said piston with said chamber, another position for connecting sald pistonwith the source of fluid pressure, and a third ,position in whichiiuid under pressure is supplied to said chamber and communication is open' from said piston tothe chamber, and

of current supplied to the motor for operating said valve means.

-means controlled by an abnormalquantity 5. The combination4 with a fluid compres-113@ Lemme K g sor and an electric motor for driving said ating said valve device, and a Huid pressure compressor, of a compressor unloading detiming means fordelaying the movement of vice including a piston operated by fluid Said valve device to cut off the supply of 10 under pressure, a valve device for controlfluid under pressure to said piston.

ling the supply of fluid under pressure to In testimony whereof I have hereunto set said piston, means operated upon a predetermy hand.

mined rise in current to the .motor for oper- BURTON S. AIKMAN. 

